Aircraft: GULFSTREAM G200 (IAI 1126 GALAXY)
Phase of flight: Initial Approach
Anomaly: Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR

At cruise; pilot flying (PF) loaded runway and approach he thought he would get. PF got up to use LAV. When he came back I sent for a new ATIS so I could check approach. When the ATIS came back I was confused about runways they were using it said 25L which we expected but it also said 19R and 19L. I said did LAX add new runways. Then we realized I had sent for LAS ATIS. Resent for right ATIS. This started us to get behind. We started to get busy with ATC instruction changing speeds and fixes. We were given direct GRAMM and couldn't find it on our flight plan so we typed it in and went direct. I reload arrival and picked PGS transition and GRAMM was there and then went direct to that GRAMM. I still needed to load approach and do approach checklist. We were given descend via and set lowest altitude. We were already past TOD and didn't notice it right away. When we realized we had passed TOD; PF clicked off autopilot to meet crossing restriction our speed got high we put out air brakes to help. I was trying to help so I never load approach. We were at RIIVR then and there was nothing in the box after that because when the PF had loaded the approach he didn't pick the RIIVR transition. While I was loading approach that is when we got off course. I finally got approach loaded with the RIIVR transition ATC noticed we were off course and we told him we were correcting. We got back on course and stable and landed safely. SoCal gave us a number to call when we got on the ground. We called when we got on ground and we explained what had happened and they seemed ok with that. They wanted us to know that we were off course. We were flying a ferry flight from to KLAX. I was the SIC flying in the left seat. At cruise altitude I sent for the ATIS for LAX to get the landing runways so I could set up the RIIVR 2 ARIVAL. I entered the ILS 25L into the FMS and got up to use the lav. While I was away the non-flying sent for the ATIS for LAX as well but typed LAS by accident and received the weather for Las Vegas. During the arrival we started going over the weather and became confused with the information not realizing the error at first. I did notice the error and the non-flying pilot did send for the correct airport ATIS. This event got us behind and I started to rush to try to help us catch up. While rushing I told the non-flying pilot that I loaded the ILS to 25L already and to expect the visual. This is where the mistake happened. When I loaded the ILS to 25L I failed to load the river transaction. When we arrived at the RIIVR fix the fixes for the transition to the ILS were not there causing us to have a nav deviation. We did get back on the ILS when we notice the problem and landed without incident. We were asked to call SoCal where we were asked what happened. They seemed ok and understood our error. Gulfstream crew was late setting up the arrival; approach; and landing runway in the FMC. As a result; aircraft was off course for a portion of the arrival.